Engineers not involved in the probe say they would look closely at the bracing system for clues to the failure. The C-470 overpass is an active roadway with constant vibration from traffic. Emphasizing that his comments are “speculative,” Frederick R. Rutz, project manager for engineering firm J.R. Harris & Co., Denver, expresses “concern that deflection in the C-470 bridge might be imposed upon the girder through the bracings.”

“That is clearly one of the things that we’re examining,” as well as the splicing of the girder and placement on the abutment and piers, says Joe Osterman, director of highway safety at the National Transportation Safety Board, Washington, D.C. NTSB is leading the investigative team comprising the Colorado Dept. of Transportation, Jefferson County Sheriff’s Dept., Colorado State Patrol, Asphalt Specialties, Ridge and AFCO.

Ridge has “never had anything like this happen,” says Dave Minshall, spokesman. Noting there was “nothing unusual about the bracing system,” he adds that the girder “was placed and braced by a plan signed off by CDOT.”